This invention relates to a starter for starting an engine such as an automobile internal combustion engine and, more particularly, to a structure for preventing a sliding portion of the starter from being contaminated with dust, water, brine, etc., and from rust occurrence, and a starter employing such a structure.
In general, a conventional starter for starting engines comprises a motor, a motor housing, a pinion shaft disposed in the motor housing and slidably supported by a ball bearing, and a mechanism including a clutch for connecting an output shaft of the motor and the pinion shaft and for projecting the pinion shaft out of the motor housing to engage with a ring gear in a transmission casing of the engine to thereby rotate the ring gear and start the engine.
In a conventional starter of this type, as described in Japanese Patent Laid-Open No. 61-1864, for example, the motor housing is simply cylindrically formed around the peripheral portion of the pinion shaft, and the ball bearing for rotatably and slidably supporting the pinion shaft is fixed to the motor housing. The pinion shaft is provided with a stepped portion at its outer periphery and inserted into the ball bearing so that the stepped portion of the pinion shaft abuts the side face of the ball bearing.
Provision of the step portion of the pinion gear abutting the ball bearing is to prevent entry of brine, dust, etc., into the sliding portion between the ball bearing and the pinion shaft so that rust occurrence will be prevented and a smooth sliding operation will be carried out.
The mechanism which accomplishes rust-proofing and dust-proofing by employing the conventional technique described above cannot completely cut off the invasion of brine, dust, etc., in an atmospheric gas when a pressure inside the transmission case rises and dirty atmospheric gas inside the transmission case flows into the motor housing. Thus, if this starter is used for several years, the sliding operation of the pinion shaft is adversely affected eventually leading to a seizure of the pinion shaft onto the bearing sliding surface. Further, in the conventional structure described above, after assembling of the clutch, the pinion shaft and the ball bearing into the motor housing, it is necessary to fix the ball bearing to the motor housing. Therefore, it is difficult to assemble the starter and the conventional technique cannot be easily applied to practical application.
Another construction is disclosed in Japanese Utility Model Laid-Open No. 64-29270 which was laid-open on Feb. 21, 1989. This construction has an air space at one side of a bearing supporting a movable pinion shaft and an opening which is formed in a front frame through which a pinion of the pinion shaft projects out of the machine frame. A radially inwardly extending flange portion is formed at the opening to provide a small clearance between an outer periphery of the pinion and the opening. The flange portion has a adjacent relation to a shoulder portion of the pinion shaft when the pinion projects outside the frame whereby a clearance between the opening and the pinion is reduced at the opening when the pinion shaft is projected outwardly of the frame.
The above construction is further provided with a drain passage for enabling a discharge of a liquid entering through the clearance into a transmission casing. Even with the above-mentioned construction, a problem resides in the fact that pressure in the air space increases over a given time period so that air in the space is likely to penetrate into a sliding portion between the pinion shaft and the bearing and contaminate the sliding portion with dust, water, brine etc. contained in the air.